Thanks comatose. We've all been warned. Hehe. I think most of us using this type of stuff went in well aware that DOW had not tested this stuff in a saltwater environment.
Trust me, I've mulled over this quite a bit and finding that many europeans have safely used this stuff for years (not only for freshwater, but also for saltwater), I decided to take the plunge and I'm carefully awaiting any deleterious effects, though I highly doubt it. Also, take into account that this stuff is inert and if it does break into small particles, should not harm anything in the tank. The great thing about this stuff is that if it ever does start causing problems, you can rip/peel the stuff right off.
Peace,
John H.